A large number of patent applications have been made for three-piece solid golf balls, but those, in particular, with a large size, superior to a two-piece golf ball in performance, that is impact resilience, flying distance and hit feeling which are important for golf balls, have not been developed yet.
For example, Japanese Patent Publication (examined) No. 61029/1988 proposes that a lower specific gravity is given to an inner layer (inner core) of a solid core and a higher specific gravity is given to an outer layer (outer shell) of the solid core to give a differential specific gravity, whereby obtaining high impact resilience and good hit feeling. For small size golf balls, the high impact resilience has been obtained because a sufficient specific gravity difference can be obtained, however, for large size golf balls satisfactory impact resilience, flying distance and hit feeling have not been obtained yet. In addition, according to Japanese Kokai Application No. (unexamined) 181069/1987, a diameter of a solid core is relatively reduced to an extent of 24 to 29 mm and a differential specific gravity is given between an inner layer having a higher specific gravity and an outer layer having a lower specific gravity to obtain increased flying distance, good hit feeling and controllability. However, impact resilience and flying distance have not exceeded those of the two-piece golf ball, which has been used at present. Furthermore, since TMPT (U.S. Pat. No. 3,313,545), which has been hardly used at present, is used in the inner layer, the three-piece golf balls according to Japanese Kokai Application 181069/1987 are remarkably inferior to the two-piece golf ball, which has been used at present, in durability.
Besides, according to Japanese Kokai Publication No. 241464/1985, a differential specific gravity is given between an inner layer having a larger specific gravity and an outer layer having a lower specific gravity in the same manner as in the above described Japanese Kokai Application No. 181069/1987 and the inner layer is made softer to reduce a moment of inertia of a ball, whereby obtaining the high impact resilience and the good hit feeling. This ball is satisfactory in hit feeling, but inferior to the two-piece golf ball in maximum impact resilience.